1. Field of the Invention
This invention relates to an improved method of connecting a monocrystallized aluminum wire or an aluminum wire including grain boundaries with a diffusion layer formed in a semiconductor substrate.
2. Description of the Related Art
FIGS. 1A to C show a conventional method of connecting polycrystalline aluminum wires formed by an ordinary sputter method with diffusion layers formed in a semiconductor substrate.
First, as is shown in FIG. 1A, element isolating regions 22 are formed on a p-type semiconductor substrate by a selective oxidation method. Then, a 10nm thick gate oxide film 23 is formed by thermal oxidation method on an element region isolated by the element isolating regions 22. Thereafter, polycrystalline silicon doped with, for example, an n-type impurity is deposited on the substrate to a thickness of about 200 to 300 nm. The polycrystalline silicon is etched by photoetching method, thereby forming a gate electrode 24 having a predetermined configuration. Then, using the gate electrode 24 as a mask, arsenic (As) which having an acceleration energy of, for example, 50 keV, is injected into the semiconductor substrate 21 to a density of about 5.times.10.sup.15 cm.sup.-2. As a result, n-type diffusion layers 25 are formed in the semiconductor substrate 21. Since this injection is performed, using the gate electrode 24 as a mask, the diffusion layers 25 are self-aligned. Next, an interlayer insulating film 26--for example, an SiO.sub.2 film--is formed on top of the entire substrate 21 to a thickness of about 500 to 1000 nm by chemical vapor phase growth method. And then, predetermined portions of the interlayer insulating film 26 are etched by photoetching method, to form contact holes 27 reaching the n-type diffusion layers 25.
Next, as is shown in FIG. 1B, an aluminum film 28 is deposited by, for example, a sputter process, on top of the entire substrate 21 to a thickness of about 500 mn. As a result, the aluminum film 28 is placed in contact with the diffusion layer 25 via the contact hole 27.
Then, as is shown in FIG. 1C, the aluminum film 28 is etched by a photoetching method, to form aluminum wires 28' having predetermined configurations.
According to the above-described method, since the aluminum film 28 is polycrystalline, electromigration and stressmigration tend to occur.
To overcome this drawback, a high-melting point metal such as tungsten (W), molybdenum (Mo), or copper (Cu) may be used as a wire in place of aluminum. However, a film made of tungsten or molybodenum is disadvantageous in that the resistance is higher than that of an aluminum film, and a film made of copper easily reacts with silicon (Si) and silicon oxide (SiO.sub.2).
Accordingly, a method has been devised wherein a monocrystalline aluminum film is formed on a substrate by CVD method. However, using this method, it is necessary to place a seed in the substrate in order to form a monocrystalline aluminum film. Hence, a high quality aluminum film cannot be formed on exposed portions of the diffusion layers and on the insulating film.